void xx() {
    RCC_APB2PeriphClockCmd(RCC_APB2ENR_TIM1EN, ENABLE);
    RCC_AHBPeriphClockCmd(RCC_AHBENR_GPIOAEN, ENABLE);

    GPIO_InitTypeDef gpio_cfg;
    gpio_cfg.GPIO_Pin = GPIO8;
    gpio_cfg.GPIO_Mode = GPIO_Mode_AF;
    gpio_cfg.GPIO_Speed = GPIO_Speed_50MHz;
    gpio_cfg.GPIO_OType = GPIO_OType_PP;
    gpio_cfg.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_Init(GPIOA, &gpio_cfg);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource8, GPIO_AF_6);

    // timer core
    TIM_TimeBaseInitTypeDef tbinit = {0,};
    tbinit.TIM_Period = 400;
    tbinit.TIM_Prescaler = 0;
    tbinit.TIM_ClockDivision = TIM_CKD_DIV1;
    tbinit.TIM_CounterMode = TIM_CounterMode_Up;
    tbinit.TIM_RepetitionCounter = 0x0000;
    TIM_TimeBaseInit(TIM1, &tbinit);
    TIM_Cmd(TIM1, ENABLE); // start the timer

    // pwm generation
    TIM_OCInitTypeDef ocinit = {0,};
    ocinit.TIM_OCMode = TIM_OCMode_PWM1;
    ocinit.TIM_Pulse = 200;
    ocinit.TIM_OutputState = TIM_OutputState_Enable;
    ocinit.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OC1Init(TIM1, &ocinit);
    TIM_OC1PreloadConfig(TIM1, TIM_OCPreload_Enable);
}